People who consume, on average, more than one alcoholic drink daily face a significantly higher risk of developing six types of cancer, according to sobering new Canadian research.
The study, published in Tuesday's edition of the medical journal Cancer Detection and Prevention, is one of the most detailed examinations of the relationship between drinking and cancer ever done. It found that moderate and heavy drinkers of beer and spirits are markedly more likely to develop cancer than teetotallers or occasional drinkers.
"The heaviest drinkers had the highest risk, whether you look at the quantity consumed or the duration of drinking," Andrea Benedetti, an assistant professor in the department of epidemiology, biostatistics and occupational health at McGill University in Montreal, said in an interview. "And the risk was really driven by beer and spirits."
Wine drinkers seem to have a slightly lower cancer risk, although Dr. Benedetti cautioned that the numbers are not solid enough to draw conclusions. "The wine part is tantalizing but a bit exploratory," she said.
In the study, a heavy drinker was one with 180 or more "drink-years" - a calculation of the average drinks per day multiplied by the number of years of drinking. For example, someone who consumes 10 drinks daily for 18 years has accumulated 180 drink-years, as has someone who consumes three drinks a day for 60 years.
The research team found that regular heavy consumption of beer and spirits - meaning 180 drink-years or more - increased the risk of esophageal and liver cancer more than seven-fold.
The risk of colon, stomach and prostate cancer was about 80 per cent higher among heavy drinkers, while lung cancer risk rose by almost 60 per cent.
Researchers examined the link between alcohol and 13 types of cancer. While the link was strong for the six types of cancer cited above, they found that drinking posed no apparent excess risk for seven other types: pancreatic cancer, rectal cancer, kidney cancer, bladder cancer, melanoma, Hodgkin's lymphoma and non-Hodgkin's lymphoma.
While much research has been published on the link between alcohol and specific types of cancer, the strength of the new research is that it looked at a wide range of cancers in a single large group, providing a good snapshot of the relative risks of various cancers.
"This study crystallizes many strands of evidence from different studies on different types of cancer and alcohol consumption," said Jack Siematycki, the Canada research chair in environment and cancer at the University of Montréal.
The findings were derived from a large occupational cancer study conducted in Montreal in the 1980s. It proved to be a treasure trove because, in addition to detailed information on things people were exposed to in the workplace, they also included information on a host of non-occupational factors such as drinking alcohol, smoking cigarettes, diet and socioeconomic status.
There were 3,571 participants in the study - all men aged 35 to 70 - who provided detailed information on their alcohol consumption. The fact that all participants were men means there are no data on breast or ovarian cancer, but researchers said the findings on other cancers should apply to women as well as men.
Roughly 14 per cent were non-drinkers, about half drank weekly and 36 per cent consumed alcohol daily.
Dr. Siematycki said people should not make drastic changes in alcohol consumption based on this research.
"If they are consuming a reasonable limit, I wouldn't advise people to cut back on alcohol based on this research," he said. "After all, there are benefits to consuming alcohol. We can't focus exclusively on the risks."
Dr. Siematycki said that "anything below seven drinks a week is fine in terms of cancer risk. Above that, you get tradeoffs."